Conventionally, there have been used various techniques for evaluating stiffness of vascular walls, such as a technique in which a beating state of blood vessels is measured with the use of a diagnostic imaging ultrasonic apparatus, a technique in which pulse-wave transmission velocity is measured, and a technique in which interference between traveling wave and reflected wave of a pulse wave that travels through a blood vessel is measured. The measurements by these techniques need large apparatuses, and therefore should be conducted as a checkup in specialized facilities such as hospitals, in practice. Further, operations of these apparatuses require specialized knowledge.
In view of this, the inventions disclosed in Japanese Patent Application Publication, Tokukaihei, No. 5-38331 A, and Japanese Patent Application Publication, Tokukaihei, No. 5-38332 A propose arterial-stiffness evaluation apparatuses using a cuff. However, the techniques according to the inventions are merely such that a pulse wave is detected from cuff pressure, and how much the amplitude of the pulse wave changes in height is evaluated.
Further, the inventions disclosed in Japanese Patent Application Publication, Tokukai, No. 2004-223046 A, and Japanese Patent Application Publication, Tokukaihei, No. 7-124129 A propose arterial-stiffness evaluation apparatuses using a cuff. These inventions propose techniques that consider a relationship between (a) a difference between internal force and external force exerted on a wall of an artery and (b) a diameter of the artery. In the techniques, the relationship between (a) a transmural pressure across a vascular wall and (b) a vascular diameter is directly derived with the use of blood pressure and amplitude of a pulse wave detected by a cuff. The techniques requires to estimate beforehand a given function that defines the relationship between (a) the transmural pressure applied to a wall of a blood vessel and (b) the diameter of the blood vessel. Accordingly, an obtainable result obviously depends on the estimated function. This causes such a problem that the ground on whether a way of estimating the function is reasonable or not is poor.